Photographic tone correction mask



Aug. 13, 1946. R, M. EVANS ET AL 5 3 PHOTOGRAPHIC TONE CORRECTION MASK Filed Dec. 12, 1942 WM 6?, MMW

ATTQRNE s Patented Aug. 13, 1946 2,405,739 7 rno'roonarmc TONE CORRECTION MASK Ralph M. Evans and Wesley T. Hanson, J12, Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey I Application December 12, 1942, Serial No. 468,777

1 Claim. 1

This invention relates to a process in photography, and more particularly to a process in subtractive color pohtography whereby there is formed a tone correction mask which when placed in registry with a color transparency effects an improved tone reproduction curve for the transparency.

In duplicating or printing transparencies, especially those obtained by the reversal process of subtractive color photography, onto a reversal process, the low contrast in the highlight regions is exaggerated by being printed onto the low contrast-highlight regions of the reversal process.

In the preparation of subtractive color photographs it is a well-known practice to make allowance for the fact that the light absorptions of the dyes or coloring materials of the process are extended to the whole visible spectrum rather than to one part thereof and in most three-color processes the dyes are not equally bad in this respect. This is generally acomplished by using the subtractive dyes in a proportion such that the gray scale will be balanced, that is, in a proportion such that the whites and blacks will be uncolored. More specifically, the general practice may be to use less yellow than magenta or cyan to compensate for the blue-light absorption of the cyan and magenta dyes, and to use less magenta than cyan to compensate for the green light absorption of the cyan dye. As a conseqence of balancing the color materials in this manner, there is generally obtained a picture having a degradation of colors, that is, the green, blue and cyan colors are too dark, and on the other hand, the red, yellow, and magenta colors are too bright.

Also, the printing from multicolored original transparencies which consist in whole or in part of dyes, the fact that the light absorption of the dyes is extended to the wholespectrum rather than being confined to one part of the spectrum makes it impossible to obtain printed records of the individual dyes simply by restricting the color of the printing light. Since in most three-color photographic processes the three dyes are not equally bad in this respect, the final result of printing such originals is to introduce unequal parts of all three records in each image which is made, regardless of the color of light used in printing or the sensitivity of the photographic materials used. The general result is to obtain a print in which the colors are degraded as above described or may even show more degradation due not only to deficiencies in the dyes in the original transparency, but also the deficiencies in the dyes used in the duplicating process.

The usual method of compensating for the deficiencies of the dyes in such processes consists in using a negative color-correction mask in conjunction with the transparency when making the printing exposure. The mask may, for example, be prepared and used as described in the prior Evan U. 8. Patent No. 2,203,653, granted June 4, 1940; Hanson U. 'Patent No. 2,294,981, granted September 8, 1942; Evans U. S. Patent 2,376,132, granted May 15, 1945, and elsewhere.

In the present invention we describe a method of preparing a color correction mask which not only corrects for the deficiencies of the subtractive dyes of the color process, but also has tone reproduction characteristics such that when a print is made from the combination of the mask with the original transparency of which the mask is a record, large improvement in the final tone reproduction of the transparency is achieved in the print or duplicate.

One object of the present invention is to provide a tone correction mask of use for improving tone reproduction during the printing of images having improper tone reproduction characteristics. I

One object of the present invention is to provide a method for the tone and color-correction of subtractive color transparencies which utilizes masks or masking images readily detachable or removable from and replaceable on color transparencies.- r

Another object is to describe amethod of making a tone and color-correction mask which is readily removable from and replaceable on a color transparency.

One object of the present invention is to provide a tone correction mask of use in black-andwhite and color photography for improving tone reproduction during printing from black-andwhite or colored images having improper tone reproduction characteristics.

Another object of the present invention, and the preferredv embodiment thereof. is to provide a tone and color correction mask of use in color photography for improving the tone reproduction and color during printing from colored images. Other objects will appear from the following description.

In general, the objects of our invention are accomplished by forming in a light-sensitive photographic element a colloid relief image, the

characteristic curve of which comprises in the straight-line portion thickness variationsof 0pposite sign to the density variations of a transparency of which it is a recordand in the shoulder portion of the characteristic curve no appreciable thickness variations of opposite sign to the density variations of said transparency, and then dyeing the relief image as required to give tone and color corrections.

In the figure of the accompanying drawing are shown by graphical representation the characteristic curves of various photographic images employed in our invention.

through a color transparency having a reproduction curve such as curve T. Curve M1 represents the characteristic curve of an image obtained by exposure through the transparency onto the unexposed area of the same photographic element as contains the image of curve M. Curve represents the corrected reproduction curve of the transparency obtanied when in printing, the image having curve M1 is used as a mask for the transparency having curve T.

Our invention will now be described with particular reference to the accompanying drawing. In a typical case to which our invention is particularly applicable, there is at hand a color transparency having a reproduction curve such as curve '1 of the drawing. In the normal process of reproducing this transparency, as for instance onto a multi-layer color film by means of the reversal process of color photography employing color-forming development, there would be obtained a print in the toe region of which the low contrast of the toe of the curve '1 would be exaggerated. This is true whether or not the usual color-correction mask is employed in the printing process. However, if a mask is prepared in the manner of our invention, the errors of tone reproduction are partially or completely'compem sated for. A mask of the required characteristics is prepared as follows: a film having a variable contrast emulsion of the type known in the art which when exposed to light of one wavelength gives low contrast, as for example, an emulsion disclosed in Carroll U. S. Patent application, Serial No. 383,379, filed March 14, 1941, and having high contrast to blue light and low' contrast to red light, is afiixed to, and so exposed to the transparency of characteristics shown in curve T through a blue filter (Wratten No. 47 filter) that substantially only those densities: of the transparency below 0.6 are recorded. In addition, the variable contrast emulsion should not be appreciably hardened and for the purpose of the present example, is dyed with a cyan dy in order that it be suitable for the formation of a gelatin relief image when red light isused as the final exposinglight. The film is then developed in a non-hardening developing solution to a gamma of about four. Following development the film is washed and dried withoutfixing-out the unexposed silver halide. The image contained therei has substantially the characteristics shown by curve M of the drawing. For use with most multicolored transparencies, agamma of the range of the order of 1 to 4 is satisfactory for this image.-

At this point if the sensitivity of the film, for

instance, to red light has been destroyed the film is resensitized' in asuitable sensitizing bath of for example the following composition:

Pinacyanol gra"ms 0.01 Alcohol (commercial 3A) cc 75 Pyridine cc 1 Benzotriazcle gram 0.1 Water to liter 1 about 05. Generally, a gamma of the range of the" order of from'OB to'0.6 iss'atisfactory for this image and the ratio of the gammas of this image to the gamma of the abov high gamma image is, therefore, of the order of 1/0.6 to 4/03. The higher the ratio selected the greater the correction imparted to the transparency.

The silver image thus obtained in hardened gelatin has substantially the characteristic curve of curve Mi'of the drawing wherein the straight line portion of the curve is a low gamma image having density variations of opposite sign to the density variations of the transparency having curve T, and the shoulder or high density region is a positive in respect to transparency T, Since the image is a positive in-the shoulder region it may be said to have no density variations of opposite sign to the density variations of the transparency in that region. Of course, associated with the low gamma silver image in hardened gelatin, is the high gamma silver image in soft gelatin, and usually the two could not be distinguished from each other.

The film now containing the high'gamma silver image insoluble gelatin and a low gamma silver image in insoluble gelatin is etched in a wellknown manner with hot water which removes the high gamma silver image and gelatin associated therewith. The resulting relief image is then bleached with acid dichromate solution to remove the silver, then fi'xe'd-out and dyed with a gray or colored dye as required;

It'follows, since the gelatin is hardened in the region of the low gamma silver image, that the relief image, before dyeing with the gray dye, has substantially the same characteristic curve as the low gamma silver image which it originally contained, that is, a curve such as M1 of the draw ing, therefore, the relief image comprises in the straight-line portion of its characteristic curve thickness variations of opposite sign to the density variations of the transparency of which it is a record and in the shoulder portion of its characteristic curve no appreciable thickness variationsof opposite sign to the density variations of the transparency.

In order to print color and tone-corrected prints from the original color transparency used in making the relief masking image, prints are made on asuitable multi-layer color film in a process such as disclosed in Marines et a] U. S. Patent 2,252,718, granted August 19, 1941, or if desired, color-separation records may be printed and used in known color processes.

It is apparent that in the above process, in-

stead of removing the silver image from the re-' lief image, if the gamma of the silver imag is I suitable for the color correction desired, the relief mask containing silver may be used for printing color-corrected prints and the silver subsequently may be removed leaving the colorless relief mask which may be dyed up subsequently if other color-corrected prints are later required.

shown by curve T1 of the drawing,'-the characteris'tic curve of the combination 'of thetransparency and the mask is greatly improved since it is generally obtained as substantially a straight line. Not only ha the mask effected an overall decrease in contrast in the characteristic curve, but in the low density region corresponding to the highlights of the transparency, the contrast has been raised sothat equal contrast is obtained throughout thelength of thechar'acteristic curve. Of course, since the exposing light for the expcsure of the final mask is preferablyselected so as to compensate for the errors in absorption of the' dyes used in the process, color correction is also affected. The choice of wave length ofexposing light depends upon whether or what correction is desired, but generally a light of longer wave length than blue is satisfactory, for example, red, green, yellow, especially substantially monochromatic yellow light, chosen according to the principles laid down in the prior U. S. Patent No. 2,294,981, granted to Hanson, September 8, 1942. In accordance with the principles of the Evans U. S. Patent 2,376,132, above cited, the final mask may also be colored in respect to the color of the light exposing it, as described therein.

In addition to the variable contrast emulsion given above we may use in our invention other emulsions such as disclosed in the Carroll application above-cited as, for instance, one giving high contrast to green light and low contrast to red or yellow light. The emulsions are, of course, unhardened and colored, for example, cyan to give low gamma relief images. Similarly, other variable contrast emulsions are suitable for use in our invention. There is little use in our process, considering the dyes used at present in color photography, for a variable contrast emulsion giving high contrast to a region of the spectrum beyond blue and low contrast to theblue region of the spectrum. This is due to the fact that the warmer colors are required for obtaining the proper color correction characteristics in the mask in the final exposure step of our process, and practically the only case where a variable contrast emulsion of low contrast to blue light would be used is in case the color process requires blue for the final exposure of the color correction mask. I

In addition to the so-called variable contrast emulsions we may use for the masking emulsion layer an emulsion such as. commonly used on positive motion picture film, that is, emulsionscapable of development. to a range of contrasts of the order of 0.3 to 4 with different developing solutions. For example, in the manner of the process above described in detail an emulsion highly sensitive to red, green, or yellow light, and unhardened and colored complementary to the final exposing light in order to yield low gamma relief images, is given a low intensity exposure through the transparency with, for example, blue light, the sensitivity for the emulsion layer and the final exposing light being chosen for the color correction desired, and development is carried out to a gamma of about 1 to 4 in a high contrast non-hardening developing solution. Without fixing, the film is again exposed with the exposing light chosen for the desired color correction and developed in a low contrast hardening developer to a range of gamma of about 0.3 to .6. The film is then etched with hot water as above described, the silver image is then removed with acid bichromate solution, and the relief image dyed up with the gray dye. The resultant relief masking image has a characteristic curve such as M1 of the drawing.

The advantages of the masks of our invention will now be apparent. Since the mask is composed of a gelatin relief image it is possible at any time to remove the dye image with, for example, dilute ammonia solution, leaving a colorless relief image on the transparency which in n way interferes with the appearance of the color transparency. It is, therefore, possible at any time to compare the original transparency with the print and later with a minimum of ing image is readily removable the invention permits return of a colored transparency to a customer without any visible alteration and should it later be desired that other tone and. color-corrected prints be made from the same transparency the attached relief mask is dyed up as required. An enormous saving in time and. materials, as well as improved quality, are thereby attained.

*In an alternative manner, and this constitutes a referred embodiment of our invention, a photographic stripping film constructed as described in Nadeau et. al., U. S. Patent 2,266,435, granted December 16, 1941, or other stripping film having a substantially water impermeable permanent support for the emulsion layer may be used as the source of the sensitive emulsion layer in which the relief masking image is formed. The sensitive film may be stripped from the stripping film and laminatedonto the color transparency with a solution of the following composition:

To which are added Turkey red oil in the proportion of 15 percent of the weight of the gelatin and glacial acetic acid to the extent of 10 per cent of the weight of the gelatin. The emulsion is then exposed and processed in contact with the color transparency to a dyed relief mask in the manner previously described, the impermeable support of the stripping film preventing the processing solutions from attacking the dye images in the color transparency. Since the mask is formed in registry with the images of the transparency, there is no problem of registering the transparency and mask before printing, whereas if the mask is processed separately from a transparency it must later be registered therewith before print- The masks or our invention may be retouched for the reasons and inthe manner described in our copending application, Serial No. 468,776 filed December 12, 1942, now Patent 2,371,746.

As above-mentioned the masks of the invention having characteristics substantially as shown by curve M1, in order to compensate for low contrast in the highlight portion of a transparency, must have little or no gradation in the shoulder region, and may actually be a positive in the shoulder region in respect to the transparency; In curve M1 the mask is shown as having decreasing density, that is, positive density gradient in the shoulder region to compensate for the low contrast in the toe of the transparency curve T.

We contemplate as within our invention tone and color-correction masks of the general characteristics described, wherein the straight-line portion of the characteristic curve is negative in respect to a transparency of which it is a record, and in which in the shoulder region there is little or no gradation of opposite sign to the transparency, and including masks with density variations of the same sign in that region. Therefore, herein and in the appended claim where we state that the masks have in the shoulder region no appreciable density variations of opposite ign to the density variations of the transparency, we mean it to be understood that this includesin the shoulder region: (1) small density variations of opposite sign to. thetransparency but'of'anorder less thannormally obtained with photographic emulsions, (2) no density gradation in the portion of the shoulder masking the toe' of the transparency; and"(3') density varyingin' the same direction as the density variations of the transparency.

Another use for which the masks of our invention are especially adapted is in projecting or viewing of color transparencies. That is, in reversal processes of color photography where colored images are formed by mean of color-forming development, images are obtained commonly having high contrast and the usually low contrast in the shoulder and toe regions (see curve 'I). A mask prepared as described is especially suitable for combining with such a transparency when it is desired to obtain the best image for viewing or projecting.

As is apparent, our invention is not limited to use in processes of color photography, however, our preferred embodiment resides therein. That is, in processes of blackand-white photography when printing from transparencies having improper tone reproduction characteristics, as for instance, from a black-and-white image having lower gamma in the toe and shoulder region-'5' of the characteristic curve-than in the straight-dine portion, a tonecorrection mask may be prepared as described which when used in printing in combination with the image of which it is a record of opposite sign, an improvement in tone reproduction is obtained. In' the past, practically the only method of improving tone reproduction in blackand-white photography has been to print an original transparency onto a process of different contrast thereby altering the overall contrast in the print but obtaining some compensation for errors in tone of the original.

In addition, our invention may be used in conjunction with printing from a colored negative transparency, as. for example, prepared from photographic elements designed as described in J elley and Vittum U. S. Patent 2,322,027, granted June l5, 1943yMannes etal. U.-S; Patents'2;304,939 and 2,304,940, granted December 15,:1942;that' is; in conjunction with color filmswhich after original exposure are immediately developed to subtractively colored dye images. In this case, the final mask is a negative record of the color negative but, of course; is a positive in respect to the final positive color print; In fact,our invention is applicable to the improvement of tone reproduction in any proces of photography wherein the image of which the mask is a record has tone reproduction errors of'the order described.

Also apparent, is the fact that the masksof my invention may be designed so as to correct not only for tone reproduction errors of the transparency being printed, but also to correct for tone reproduction errors introduced by the duplicating process. This is accomplished by giving the mask a shoulder gamma compensating for tone errors of both the toe of the transparency and any toe introduced in the duplicating process.

Our invention having thus been described we would have it understood that the disclosure herein is by way of example, and that we consider as included in our invention all modifications and equivalents falling within the scope of the appended claim.

What we claim is:

A photographic element comprising a photo graphic color transparency having low contrast in the regions of high and low exposure and high contrast in the regions of intermediate exposure, and in registered printing relation therewith as a tone and color-correction mask, a colloid relief image having a characteristic curve whose straight line portion has density variations" of opposite sign to the density variations of the regions representing intermediate exposiu'e in the transparency, and whose shoulder portion has density variations of the same sign a the density variations of the regions represented by the toe of thecharact'eristic curve of the transparency.

RALPH M. EVANS. WESLEY T. HANSON, JR. 

